The Session Initiation Protocol (SIP), being a part of an Internet Engineering Task Force (IETF) standard process, is used for setting up, modifying and terminating a multimedia session between messaging users in an IP network. The multimedia session includes Internet multimedia meetings, calls in the IP network, and multimedia publishing. SIP is a text-based signaling control protocol that works in client/server mode. SIP servers are categorized into stateful servers and stateless servers. A stateful server may store received, returned or forwarded messages, while a stateless server can only receive, return or forward messages, and cannot store these messages.
In the conventional art, an IP multimedia subsystem (IMS) is a standard system supporting IP multimedia services and independent of access technologies. The IMS is a SIP-based system, which establishes, manages and terminates various multimedia services by using a SIP call control mechanism.
To provide messaging users with better mobile data service experiences in heterogeneous networks among which differences exist in service package subscription, terminal capability and lower layer network environment. The current specifications support the development of mobile data services under a multi-device condition in the IMS. The multi-device condition means that a user ID corresponds to multiple terminals of the user, in which the user may communicate by using any of registered terminals. A user with multiple terminals is called a multi-device user.
In the conventional art, a multi-device user obtains device information based on the presence service. A presence server receives SIP PUBLISH requests from different terminals of the multi-device user. Each SIP PUBLISH request is intended to publish a presence information document including the presence information of the user, service and device. The presence server sends the obtained presence information to the requesting terminals through a SIP NOTIFY message. Any of the multiple terminals of the user plays two roles: a presence source, which is responsible for publishing information related to the terminal to the presence server; a presence information watcher, which is responsible for subscribing to the presence information of other terminals.
During the implementation of the invention, the inventor discovers that the user obtains terminal device information by subscribing to the presence information published by the presence service in the conventional art and that the conventional art has the following problems: When a multi-device user browses the presence information of other terminals by using one of the terminals, each terminal is identified by a unique terminal identifier (deviceID) allocated by the presence server, where the terminal identifier complies with the format of a universally unique identifier (UUID) defined in the conventional art. However, the multi-device user cannot easily differentiate and remember such identifies, and may be easily confused when browsing the presence information of multiple terminals. In addition, the multi-device user needs to transfer sessions between different terminals. Thus, the multi-device user must know state information such as the ID of a session in the source terminal and capability information of the target terminal. The presence information, however, indicates whether a terminal joins a session only, but does not indicate the state information of the session or the capability information of the terminal device. Therefore, the multi-device user cannot transfer sessions in other terminals to the current terminal.